Vitamin K: Sources, Health Benefits, Deficiency, Side effects, RDA
In this article, we are exploring Vitamin K – a group of compounds such a Vitamin K1 and Vitamin K2.
✅ Researched Based: This article is based on research. Number’s in Brackets are links to research papers and Scientific articles from well-established and authoritative websites (all links open in a new window).
What is Vitamin K
Vitamin K is a nutrient essential for life and health. It is involved in many important body functions, such as preventing blood clotting and maintaining healthy bones.
It is one of the most basic fat-soluble vitamins, i.e. it requires the presence of fat in order to be absorbed by the body.
The term vitamin K refers to a group of molecules with a similar chemical structure and action. In its natural form it is found in a wide variety of foods and in food supplements.
Vitamin K is classified into two main forms, vitamin K1 (phylloquinone) and vitamin K2 (menaquinone).
Vitamin K1 is mainly found in plant sources, such as green leafy vegetables (spinach, broccoli, lettuce, etc.), vegetable oils and certain fruits (blueberries, figs, etc.).
Related: Vitamin C: Sources, Health Benefits, Deficiency, Side effects, RDA
In contrast, vitamin K2 is mainly of microbial origin. Much of the daily vitamin K requirements in humans are produced by gut bacteria in the form of K2.
In nature, menaquinone is present in moderate amounts in animal products such as meat, milk, soy or eggs, and in fermented products such as traditional Natto food.
Although both types of vitamin K are equally beneficial to health, vitamin K2 (menaquinone) appears to have greater potency.
Unlike the other fat-soluble vitamins (A, D, E), vitamin K circulates in small amounts in the blood, as it is metabolized very quickly and then excreted. This means that when we ingest vitamin K1, only 30% to 40% is retained in our body, with the remaining 60 to 70% being eliminated through urine and stool.
Vitamin A Daily Requirements
Vitamin K requirements by age group are shown in the table below:
| Age | Men | Women | Pregnancy | Breastfeeding |
|---|---|---|---|---|
| Birth – 6 months | 2,0 μg | 2,0 μg | – | – |
| 7 – 12 months | 2,5 μg | 2,5 μg | – | – |
| 1 – 3 years | 30 μg | 30 μg | – | – |
| 4 – 8 years | 55 μg | 55 μg | – | – |
| 9 – 13 years | 60 μg | 60 μg | – | – |
| 14 – 18 years | 75 μg | 75 μg | 75 μg | 75 μg |
| 19+ years | 120 μg | 90 μg | 90 μg | 90 μg |
Vitamin A Foods
Foods that are considered good sources of vitamin K (in the form of vitamin K1) are vegetables, especially green leafy vegetables, while we can also get it from certain vegetable oils (e.g. soybean oil, rapeseed oil), fruits (kiwi, dried figs, avocados, blackberries, grapes, pear, mango, papaya) and nuts.
Meat, dairy products and eggs contain vitamin K1 at low levels, but vitamin K2 is found at higher levels in these foods. Also, fermented cheeses contain vitamin K2.
In more detail, the table below shows the vitamin K content of certain foods (mainly vitamin K1, unless the vitamin K2 content of the food is indicated in a note):
| Foods | Amount | Vitamin K (mcg) |
|---|---|---|
| Vegetables | ||
| Kale, cooked | 125 mL (½ cup) | 561 |
| Kale, raw, chopped | 250 mL (1 cup) | 499 |
| Spinach, cooked | 125 mL (½ cup) | 469 |
| Dandelion greens, raw, chopped | 250 mL (1 cup) | 452 |
| Mustard greens, cooked, chopped | 125 mL (½ cup) | 438 |
| Collards, cooked, chopped | 125 mL (½ cup) | 408 |
| Beet greens, cooked | 125 mL (½ cup) | 368 |
| Swiss chard, raw | 250 mL (1 cup) | 316 |
| Dandelion greens, cooked | 125 mL (½ cup) | 306 |
| Swiss chard, cooked | 125 mL (½ cup) | 303 |
| Turnip greens, cooked | 125 mL (½ cup) | 280 |
| Parsley, raw | 60 mL (¼ cup) | 260 |
| Collards, raw, chopped | 250 mL (1 cup) | 166 |
| Beet greens, raw | 250 mL (1 cup) | 161 |
| Lettuce, spring mix (mesclun), raw | 250 mL (1 cup) | 154 |
| Spinach, raw | 250 mL (1 cup) | 153 |
| Endive and escarole, raw, chopped | 250 mL (1 cup) | 122 |
| Brussel sprouts, cooked | 4 sprouts | 118 |
| Broccoli, cooked | 125 mL (½ cup) | 116 |
| Radicchio, raw, shredded | 250 mL (1 cup) | 108 |
| Lettuce, green leaf, raw, shredded | 250 mL (1 cup) | 103 |
| Broccoli, raw, chopped | 250 mL (1 cup) | 94 |
| Watercress, raw, chopped | 250 mL (1 cup) | 90 |
| Bean sprouts, soybean, raw | 125 mL (½ cup) | 70 |
| Lettuce, romaine, raw, shredded | 250 mL (1 cup) | 61 |
| Cabbage, raw, shredded | 250 mL (1 cup) | 56 |
| Green or scallion onion, raw, chopped | 60 mL (¼ cup) | 55 |
| Asparagus, cooked | 6 spears | 46 |
| Fruit | ||
| Kiwifruit | 1 medium fruit | 28 |
| Rhubarb, cooked | 125 mL (½ cup) | 27 |
| Blueberry, frozen | 125 mL (½ cup) | 22 |
| Avocado | ½ fruit | 21 |
| Other | ||
| Pork liver | 75 g (2 ½ oz) | 66 |
| Sausage (pork, veal) | 75 g (2 ½ oz) | 53 |
| Tuna, light, canned with oil | 75 g (2 ½ oz) | 33 |
| Soybeans, cooked | 175 mL (¾ cup) | 24 |
| Matcha green tea powder | 2 g of tea powder | 60 |
Vitamin A Health Benefits
One of the best known proteins that depends on the action of vitamin K and is directly involved in blood clotting is prothrombin (clotting factor II).
Osteocalcin is another vitamin K-dependent protein found in bone and regulates calcium deposition in bone, and it appears that the presence of vitamin K is essential for its synthesis.
In addition, vitamin K is absorbed from the small intestine, participates in lipid metabolism and is transported to the liver, where it is repackaged into very low-density lipoproteins (VLDL).
Many of the proteins involved in the formation of clotting need vitamin K for their proper action. Without the required amount of vitamin K there is an increased risk of bleeding.
Taking vitamin K prevents calcium deposition in the vessels and tissues, it is suggested that it indirectly participates in cardiovascular protection [x]. However, larger and better designed studies are needed to highlight the role of vitamin K in preventing cardiovascular disease.
According to studies, people who consume large amounts of vitamin K through food or supplements have stronger bones and are less likely to suffer a bone fracture in their lifetime even if the individuals already had osteoporosis [4].
The action of vitamin K is enhanced by the action of vitamin D, which is why it is recommended to be taken together for better absorption of calcium by the bones.
In recent years, more and more studies have shown that vitamin K has anti-inflammatory properties, protecting brain cells from oxidative stress and the harmful effects of free radicals. [6]
Vitamin K Deficiency
Vitamin K deficiency is not common and can only occur in people who have malabsorption problems or liver disease. In healthy people, whose diet is varied, it is almost impossible to achieve a low intake of vitamin K so that blood clotting is affected.
However, in case of vitamin K deficiency, the activity of prothrombin in blood is significantly reduced, resulting in bleeding. Similarly, deficiency of this vitamin may lead to the development of osteoporosis. The groups at risk of vitamin K deficiency are:
- Newborns and infants who are not given vitamin K supplementation in the first weeks (2nd – 12th) of life (due to low vitamin K1 transfer to the placenta, low levels of clotting factors and low vitamin K content in breast milk.
- People with malabsorption disorders (e.g. cystic fibrosis, celiac disease, ulcerative colitis, short bowel syndrome);
- Patients who have undergone bariatric surgery;
- People taking medications that interfere with vitamin K metabolism;
*Vitamin K Toxicity effects are unlikely to occur due to increased vitamin K intake [7].
Related: Best Vitamin B Complex Supplement & Everything You Need To Know In Between
Vitamin A Pregnancy
Vitamin K is particularly important during pregnancy, especially in cases of premature birth. All premature babies show symptoms of haemorrhagic syndrome, more or less severe, related to the availability of vitamin K.
In particular, premature babies are likely to have a marked vitamin K deficiency, their intestinal tract may not be inhabited by those micro-organisms that synthesize vitamin K and the vitamin K stores in their liver may be inefficient.
Consequently, vitamin K supplementation may contribute significantly to the prophylaxis of premature infants from complications due to haemorrhage.
Vitamin K, which is naturally present in human breast milk, has been shown to be inadequate relative to that required by infants less than 6 months of age. Supplementation during breastfeeding improves the vitamin K content of breast milk and reduces the potential for neonatal haemorrhage.
Vitamin K Supplements
Below are some of the best Vitamin K supplements that you can buy online or via your local pharmacy.
Final Take
Vitamin K is important for protein synthesis, strong bones, brain and blood clotting. If you eat your vegetables, you probably don’t need a supplement.
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